Dysplasia is a marker of malignant potential and a determinant of surveillance colonoscopy intervals, and therefore, provides a meaningful division for the categorization of serrated polyps. Dysplasia can occur in at least two forms in serrated polyps: conventional cytological dysplasia similar to that which occurs in conventional adenomas, and serrated dysplasia. Cytological dysplasia is seen in a subset of SSA/SSP,
suggesting a more aggressive phenotype, and such lesions are referred to as SSA-D/SSP-D. The term “mixed polyp” was previously used for these lesions, but is no longer recommended. Although TSA might also display conventional cytological dysplasia, they are mostly characterized by serrated dysplasia.2 Serrated dysplasia does not demonstrate markers of proliferation, such as increased mitosis or staining with Ki67. Rather, the cells appear senescent, Pembrolizumab research buy with abundant eosinophilic cytoplasm. When conventional dysplasia is also seen in a TSA, an increased likelihood of malignant conversion is assumed. A unique property of TSA is ectopic crypt formation. This offers a more definitive feature for its recognition, as well as an explanation selleck chemicals for the exophytic growth of TSA compared to SSA/SSP, where this feature is not observed.
It has also been suggested that this loss of anchorage of the crypt base in TSA is a reflection of molecular differences between TSA and SSA/SSP, which reflects the genetic program of mucosal development underlying TSA.2 The process whereby a serrated polyp undergoes malignant transformation is widely referred to as the “serrated pathway”. Within this field of study, the “canonical serrated pathway” is perhaps the best known, and has been proposed to explain STK38 the progression of an SSA/SSP through SSA-D/SSP-D to a colorectal cancer.4 SSA/SSP have high rates of somatic BRAF mutation, and widespread DNA methylation known as CpG island methylator phenotype. Cancers arising from SSA also show these molecular features,
and comprise an estimated 15–20% of the total colorectal cancer burden.5 Both SSA and SSP, and the cancers they give rise to, are concentrated in the proximal colon. Less is known about the pathway to colorectal cancer associated with TSA, and as yet, this pathway has no definitive steps. The differentiation of SSA and TSA at the morphological level has been facilitated by studies of their fine structure. Molecularly, TSA do not demonstrate unique features, and can harbor somatic mutations in BRAF or KRAS or neither of these. They are not highly methylated and are concentrated in the distal colon. The senescent appearance of a TSA highlights a possible defect in the rate of apoptosis in these lesions, but to date, there is no single gene mutation has been assigned to this particular pathway, and further genetic/epigenetic molecular markers would be of value. Mutations in mitochondrial DNA (mtDNA) have been associated with defects in apoptosis.